Multiple Shopify store owners report a persistent bug where customers select a product size (e.g., XL), but the cart defaults to the smallest size option (typically Small) instead. This issue has been occurring for at least 2+ years across different stores.
Key characteristics:
Appears random: not tied to specific sizes, devices, or browsers
Always defaults to the first variant in the list
Affects only some items in multi-item carts
Reported across multiple themes (Venture, ICON 2.0, BOOST) and device types
Some users report it happens primarily on mobile devices (Samsung browser, Apple iPhone)
Attempted solutions (unsuccessful):
Multiple Shopify support escalations to senior staff
Deleting apps
Switching themes multiple times
Theme developer consultations
Current status:
No confirmed solution has been found. One user suspects Shopify’s “add first variant by default” setting may be involved, but this remains unverified. The issue continues to cause lost revenue and customer frustration, with at least one store owner considering migrating to another platform.
Summarized with AI on October 26.
AI used: claude-sonnet-4-5-20250929.
So two or so years ago I switched from Shopify Plus back to a regular Shopify plan when our business took a nose dive. Shortly after we started to notice random customers reporting that they were getting the wrong product sizes. If someone wanted a XL t-shirt they ended up with a small which is the first option for sizing. Customer selects the product option they want, clicks the add to cart button and then a small ends up in the cart. After a few more people reported this we started to log all of the cases and it looks to be completely random and not related to a size, device, or browser however a small which is the first product option always seems to be what this bug reverts to. A customer can have a few shirts in their cart and it may only happen to one of the shirts in the cart. One person said they noticed the bug, removed the item from their cart and tried to add it 4 more times and each time it went to small. It’s only the ‘Size’ product option.
WHAT I’VE TRIED
I’ve contacted Shopify support 3 times now over the past 2 years and each time they say they are unable to figure out what the problem is. Each time after reviewing they send the ticket to a senior support person and they still didn’t find anything.
I’ve deleting apps thinking it was related to one of those but still we have not been able to fix the problem.
I’ve switch Shopify themes twice since this started happening. All themes from different companies.
CONCLUSION
At this point I am lost and have no idea what else to do. This bug is costing me serious money and customers. I find it hard to believe that I am the only person who is experiencing this problem. If anyone else has or is seeing this can you please let me know? At this point I’ve already started building another site on another platform but moving over 900+ products is going to be a massive pain. Any help anyone can give would be greatly appreciated.
On my clothing website each item has a number of size options.
When customers are choosing their size, the website defaults to the smallest size even though they click on their desired size.
It does this many times per day on a large proportion of my orders. Please advise what I can do to stop this happening.
I know a number of other Shopify stores have this same problem. PLEASE FIX.
Thank you,
Janice Grey
I see lots of people seem to be having the issue of when a customer chooses a product size, after adding it to the cart, the size is defaulted back to the first size in the list. For example…if you choose a size XL, add it to your cart, go to cart, you will see that it now is back to Small, which is the first size variant in the list?
I have also asked Shopify, and the developer of the theme BOOST…anyone have any luck figuring this out?
I just checked your website and tried adding multiple sizes in the cart and everything worked perfectly fine, can you maybe elaborate exactly about your problem?
We’ve noticed a recurring issue where customers are ordering multiple items such as three XLs and then including one item in a much smaller size, like a Small or the smallest available option. When we follow up, they often respond that it was a mistake and that the smaller size was meant to be an XL as well. Initially, we thought it might just be user error, but it’s happening so frequently that we’re starting to suspect there may be a problem with the ordering system.